[Background and Objective]: Knowledge on the effect of alcohol consumption on the gut microbiota is scarce, and seems to be different depending of the amount of alcohol intake. Thus, this work aims to assess the effect of the amount of alcohol intake on the microbiota from healthy adults. [Methods]: 261 Spanish (25–45 y) (51% males, 49% females) and 229 Slovenians (42% males, 58% females) healthy adults were studied. Volunteers’ alcohol consumption habits were analysed by using a validated questionnaire, and classified according to their alcohol consumption: 1) None-Low (N = 124 and N = 95): <5 g alcohol/d; 2) Moderate: between ≥5 g/d and ≤20 g/d (men) or ≤12 g/d (women) (N = 99 and N = 67); and 3) High: >20 g/d (men) or >12 g/d (women) (N = 38 and N = 67). Gut microbiota was analyzed through 16S rRNA gene amplicon sequencing (V3+V4 gene regions. MiSeq 2x250 Illumina) and taxonomic analysis. General lineal models and Kruskal-Wallis plus Mann-Whitney tests were performed. [Results]: Gender differences were observed in both countries.
Women showed higher levels of Firmicutes (P = 0.001) and lower levels of Bacteroidetes families than men. The High group showed higher levels of Ruminococcaceae (P = 0.013) in Slovenians, and Fusobacteriaceae (P = 0.028) and Spirochaetes (P = 0.001) in Spanish than Moderate and None-Low. Other families differences varied between men and women in each country. [Conclusions]: The amount of alcohol intake affects the microbiota composition in a different way depending on sex and country, thus suggesting that not only sex but also environmental factors should be considered to disentangle the influence of alcohol
consumption on the microbiota from healthy adults.